Bühlmann ZH-L16C Algorithm
Dive tables, tissue compartments, coefficients and Gradient Factors used by modern dive computers
Bühlmann ZH-L16C quick access
Explore the Bühlmann ZH-L16C decompression model through coefficient tables, tissue half-times, Gradient Factors and practical explanations for recreational and technical diving.
⚠️ Warning — Data for informational purposes. This model underpins modern dive computers. Manual calculations do not replace a dive computer or proper training. Learn more about gas laws.
Model developed at the University of Zürich. Bühlmann-based algorithms are used in many modern dive computers, with implementations varying by brand and model.
What is the Bühlmann ZH-L16C algorithm?
The Bühlmann ZH-L16C algorithm is one of the most widely used decompression models in modern scuba diving. It estimates how inert gases such as nitrogen and helium are absorbed and released by the body during a dive. The model is divided into 16 theoretical tissue compartments, each with its own half-time and pressure tolerance.
ZH-L16C is especially important because it is commonly used in dive computers, often combined with Gradient Factors. These Gradient Factors allow divers to adjust the conservatism of the decompression profile by modifying when stops begin and how close the diver can approach the original Bühlmann limits.
On this page, you can compare the ZH-L16A, ZH-L16B and ZH-L16C coefficient sets, review nitrogen and helium half-times, and understand how Gradient Factors affect decompression planning.
Example ZH-L16C coefficients
In the ZH-L16C model, each tissue compartment has a nitrogen half-time,
helium half-time and specific a and b coefficients.
These values define how much inert gas pressure a compartment can tolerate
during ascent.
Very fast compartment, commonly associated with a 4-minute nitrogen half-time.
Often important for standard recreational dives and common no-decompression profiles.
Relevant for repetitive dives, long exposures and decompression planning.
The complete coefficient table above allows comparison between ZH-L16A, ZH-L16B and ZH-L16C.
Calculation formula
P = P₀ + (Pᵢ - P₀) × (1 - e^(-t × ln2 / t½))
P₀ = initial tension, Pᵢ = inspired pressure, t = time, t½ = half-time
Understanding the Bühlmann ZH-L16 Model
The Bühlmann ZH-L16 model, developed by Dr. Albert A. Bühlmann at the University of Zürich, is the most widely used decompression algorithm in the world. It forms the computational basis of virtually all modern dive computers (Suunto, Shearwater, Garmin, Mares, Scubapro, etc.).
The 16-compartment principle
The model simulates 16 tissue compartments with half-times ranging from 4 minutes (fast tissues like blood) to 635 minutes (slow tissues like bones and cartilage). Each compartment absorbs and releases nitrogen (or helium) at a different rate. The "a" and "b" coefficients define the maximum pressure tolerated by each compartment before bubble formation.
ZH-L16A, B, and C variants
The ZH-L16A variant is the original theoretical version calculated by Bühlmann, the least conservative — generally not used as-is for diving. ZH-L16B is a modified version (lower "a" coefficients on middle compartments) intended for printed tables. ZH-L16C is slightly more conservative on several compartments and is the reference variant used in modern dive computers. Gradient Factors (GF Low/High) allow divers to adjust conservatism to their preferences.
Bühlmann vs MN90, RGBM and DSAT
Bühlmann vs MN90
The MN90 tables are mainly used in the French diving system and are based on a different decompression approach. MN90 is table-based, while Bühlmann ZH-L16C is widely used inside programmable dive computers. Both models aim to manage inert gas loading, but their parameters, assumptions and practical outputs can differ.
Bühlmann vs RGBM
RGBM models add bubble-control concepts to decompression planning. Bühlmann, by contrast, is a dissolved-gas model. In practice, many divers prefer Bühlmann ZH-L16C because it is transparent, well documented and adjustable through Gradient Factors.
Bühlmann vs DSAT
DSAT is another recreational diving algorithm historically used by some dive computers. It can be more liberal on certain recreational profiles, while Bühlmann ZH-L16C with conservative Gradient Factors is often preferred for technical and mixed-gas diving.